Surface wave transmission line



Nov. 13, 1956 A. G. CLAVIER x-:T AL

SURFACE WAVE TRANSMISSION LINE 2 Sheets-Sheet l Filed May 23, 1950 Nov.13, 1956 A. G. CLAVIER ET AL SURFACE WAVE TRANSMISSION LINE 2Sheets-Sheet 2 Eiled May 23, 1950 gli mmf

E N R O INVENTORS United States Patent f SURFACE WAVE TRANSMISSION LINEAndre G. Clavier, Nutley, N. J., and David L. Thomas,

Lee, London, England, assignors to International Standard ElectricCorporation, New York, N. Y., a corporation of Delaware Applicaon May23, 1950, Serial No. 163,581k

Claims. (Cl. 333-95) 'I'his invention relates to microwave transmissionsystems and more particularly to a single wire guide line for microwavetransmission and means for coupling such lines to other forms ofmicrowave transmitting structures.

In addition to the transmission of microwave energy over radio links,coaxial cables and dielectric waveguides, it has recently beendiscovered that such high frequency energy covering a very Wide band maybe transmitted by means of a single wire properly insulated, thetransmission of energy being confined closely adjacent the wire in theelectric rand magnetic fields formed thereabout. While it was known thatwhen a wire had electric energy applied thereto that electric andmagnetic fields formed aboutthe wire, it was believed that these fieldsradiated outwardly without any definite limits or boundary. It hasrecently been discovered however, that if the conductor is coated with agiven thickness of insulation the electromagnetic fields produced bymicrowave energy are concentrated and substantially confined within agiven radius about the conductor, this radius being determined by thesize of the conductor, the quality and thickness of the insulatingcoating. By way of example, Ian ordinary No. `l2V enameled copper wirewas found to have for microwave energy in the neighborhood of 5000 mc.an electromagnetic ield concentrated within a three to four-inch radiusabout the wire and that microwave energy could be propagated in thisield closely adjacent the surface of the wire at a velocity slightlyless than the speed of light. This manner of propagation now referred toas surface wave transmission presents very small loss and-issubstantially free from electrical and other disturbances Where thisconfined field is substantially unobstructed.

One of the objects of this invention is to provide another form ofsingle wire guide line for microwave surface transmission. v

Another object of the invention is to provide a coupling device forsingle wire guide lines to effect transfer of microwave energy betweenthe guide line and other microwave transmission structures.

One of the features of the invention comprises a variation in the mannerof distributing the insulation along the line. While it is known that aninsulation coated conductor functions as `a guide line for microwaveenergy, I accomplish this distribution by disposing along a wireconductor a plurality of beads of insulating material spaced atintervals along the conductor. It is also within the scope of myinvention to provide in Ianother form a continuous coating of insulationtogether with beads in the form of enlarged sections of insulatingmaterial spaced at intervals therealong. While it is believed preferableto provide the conductor with a distribution of insulation along thesurface thereof similar propagation may be obtained along bare wirewhich presents a finite resistivity comparable tothat of ordinary copperwire. with a coating of insulation is believed to further concentratethe field closer to the surface of the wire.

Anotherl feature of the invention lies in the coupling arrangement forcoupling a guide line to the wall struc- Such wire Patented Nov. 13,1956 tures of coaxial lines and dielectric waveguides. The end portionof a hollow conductor, which may comprise a part4 or a continuation ofthe walls of a dielectric wave'- guide or the outer conductor of acoaxial line, is decreased in conductance gradually, tothe terminal endthereof. The purpose of this terminal resistance is to absorb terminallosses rather than permit radiation thereof, Iand thus provide improvedtransformer matching. .This decrease of conductance may be accomplishedby different arrangements, one example being the tapering of thethickness of the end portion of the hollow conductor below the`effective skin conducting thickness of the conductor for a lengththereof at the terminalend, and a second example being the continuationof the hollow .conductor in constant thickness but decreasing in theconducting consistency thereof until the conductivity is reducedsubstantially to zeroy at the terminal end. A third example may.comprise the spraying of the end portion of the hollow conductor boththe inside and outside surfaces, with resistance material, theresistance layer being decreased gradually'away from the end of theconductor.

The terminating insulating material at the end portion of thehollowconductor, whether or not the conductor has a terminating resistance, ispreferably enlarged in quantity and/ or quality to constrict thefieldto-a radius equal to or less than the radius of the hollowconductor. This insulating material is decreased in amount'from theterminal end thereof for a distance outwardly along the lin'e conductor,and may comprise, for example, a solid'body of dielectric material or aplurality of beads or discs of insulating material of selected sizes andspacingto produce the desired variation in dielectricquality. The beadsmay vary in cross-sectional dimensions or they may vary in length or in-both cross-section and length. The terminating insulating material mayalso be decreased in insulating quality for a distance along the lineconductor inwardly of the outer conductor. All of these arrangementsoperate to confine the electromagnetic field closely adjacent the guideline conductor for transfer of propagated microwave energy with aminimum of wave perturbation along the line and between the line 'andthe walls of microwave transmission structures.

The above-mentioned and other features and objects of this invention`and the manner of attaining them will become more apparent and theinvention itself will be best understood, by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

Fig. l is fa longitudinal cross-'sectional View of a coupling device forcoupling -a line conductor to a coaxial Fig. 2 is a cross-sectional viewtaken along line 2 2 of Fig. l v

Fig. 3 is a longitudinal sectional view of a modified form of couplingdevice employing beads of insulating material spaced along the conductorline rat the coupled end thereof;

Fig. 3A is an enlarged cross-sectional view of one of the beads `shownin Fig. 3;

Fig. 4 is a longitudinal sectional view of another embodiment of theinvention showing the distributed insulating material of the line in theform of beads with the line coupled to a `dielectric: waveguidestructure; 'and Y Figs. 5 and 6 show in longitudinal section still othermodifications of coupling devices. A

In Figs. l and 2, a single line conductor 1 is show-n of the formcomprising a conductor wire bearing .a continuous coating of insulation'2 which may be of enamel, polystyrene, polyethylene or other insulatingmaterial. The coating 2, however, may Abe omitted Where the conductorhas the prerequisite resistivity to concentrate theelectromagnetic'field within a satisfactory radius about the conductor.The :conductor '1 .is extended into `a hollow conducto-r l3 of acoupling device which may comprise the terminal end of a coaxial line -4of the ysolid dielectric type, the conductor 1 being connected as `acontinuation of the center conductor `5 of coaxial line. The hollowconductor 3, of course, may be the -wa'll portion of ea dielectricguide, such as indicated in Fig. 4. The insulating coating 2 preferablymerges or enters into a body of insulation 6, 7 which is disposed withinthe end portion of the hollow yconductor 3. The body of insulation maybe made as a single unit or in two or more parts, such as longitudinalhalves, thirds or quarters, Aand held together by a solven and/or theencircling end of the perturbation of the wave propagation at thecoupling hollow conductor 3. in Figs. 1V and 2, lfor example, the

body is shown in halves 6 and 7, grooved to receive the line conductorl1.. Where the conductors 1 and l5 are of different size, the connectingportion is preferably tapered. The hollow conductor '3 is provided witha terminal end extension 8 which preferably overlaps the body 6, whichis decreased gradually to zero conductance Aat the terminal end 9thereof. This extension K8 may be formed by tapering the thickness -ofthe conductor -3 so that the conductance thereof is decreased graduallybelow the normal skin conductance of the conductor until it reacheszero. The section `8 may be formedv by spraying Iconductive materialonto the body '6, 7 making the coat-ing thereof Vgradually thinnerunt-il the terminal end 9 comprises spaced particles of conductivematerial. The portion of the body `6, 7 extending outwardly of theterminal end 9 is tapered gradually down to the size of the coating 2.

. In Fig. 3 theinsu-lating coating 2 has disposed thereon a plurality of-beads of insulating material spaced at intervals along the Ilineconductor 1, as indicated at 10, 111, 12 and 13. These beads 410, 1 1,12 and -13 are shown to vary in diameter, the largest being the bead 10at. the termi-nal end 9 of the hollow conductor 3. The thickness orlength d of these beads preferably are much smaller than `the wavelengthof the microwave energy. The bead 10 preferably closes the terminal endof the member '3 while the 'beads 11, lf2 and 13 lare progressivelysmaller in diameter, the bead 13 closely approaching the diameter of thecoating 2. .The coating 2 may be discontinued .between Ithe first bead13 and the flinal bead 10, and also along the line conductor ifdesired', but .as shown in Fig. 3 4it is lapplied to the conductorthroughout this length. The coating 2 which preferably :is increased inthickness by an added layer of enamel serves to maintain the `beads inlposition as well as to assist in confining the electromagnetic fieldyclosely adjacent the conductor 1. The -number of 4beads `10-13 :as wellas the .spacing thereof, may be vari-ed as desired. The center conductor5 is supported by beads i1'4 in the usual manner of -coaxial lines. v

In Fig. 4 a dielectric guide 15 is vshown to include a hollow conductorl16 into which line conductor 1A extends, kthe latter beingV anchoredforV tensioning purposes conductor 1A is electrically connected by wiregripping ngers 18 of tubular sleeve 19 secured in end` cap 120 on rthehollow conductor. 16. The sleeve "19 insures proper coaxial positioningof the line conductor. In communication with the hollow conductoi 1-6 isa dielectric guide 21 for transfer of microwave energy to thelineconductor 1A which may or may not be bare lof insulation opposite thedielectric guide 21, a transition connection 22 being provided foreither direct connection to the conductor or in capacity couplingarrangement therewith.

The line conductor IlA as shown is a bare wire provided ywithdistributed insulation i-nY the form ofy beads 23 the spacing S ofwhich' is preferably inthe orderof 10S'per wavelength.. At the terminalcouplingthe beads are of 'different radial sizes, similarly asindicatedl in Fig. *3. The largest bead 24 is preferably` disposed `at'the terminal endy to close the hollow conductor. To reduce at spacedintervals along the conductor inside the hollow conductor 16. Theterminal end portion 26 `of the hollow conductor 16 is shown in thisembodiment to be of constant thickness las distinguished from thetapered thickness of the end portions 8 `in Figs. l and 2. The materialof section '26, however, is so chosen to vary in conductivity throughoutits length until the conductance of the section is substantially zero`at the terminal end thereof. This may also be `accomplished by sprayingresistance material on the inside -and/or outside surfaces of the hollowconductor, the resistance coating being ythickest at the terrninal end.

In Fig. 5 the line yconductor 11A is the Isame as shown in iFig. 4, thedistributed insulating material being in the form of beads 23 spaced atintervals therealong. These beads by proper spacing provide the sameconstricting effect upon theelect-romagnetic held as the continuouscoatingl 2 of Figs. 1 and 2. As the conductor 1A approaches .andvextends into the hollow conductor l16 the beads are spaced closer andcloser together as indicated at 127 until the shortest `spacing occursat the terminal end ofthe hollow conductor and therebeyond the usualcenter conductor spacers 114 are employed to coaxially position the lineconductor. This concentration of insulating-material at the terminal endeffectively constricts the electromagnetic field to a cross-sectionalvolume corresponding to the cross-section of the interior of the hollowconductor 16.

Referringto IFig.` 6, the terminal insulating material is shown in theform of beads 28, 29, 30 and 31, which vary both in diameter and length,and, therefore, also in spacing; adjacent the termi-nal end of the'hollow conductor 32. The largest bead28 which preferably is less inylength than the wavelength of the microwave energy, is disposed in; thetermina-l end portion 33. Additional insulating beads 34. whichareprogressively decreased in :length to the lengthofy the usual centerconductor spacer beads 35 and. areV intenposedbetween the terminal bead28 and the rstspaced bead 35. Y

While the various formsy illustrated indicate,. particularly in Figs. 3through 6, `a limited number of insulating. beads as forming theterminating insulating material for. the ligne conductor, it willv beunderstood that the number, sizes andi-actual spacing of these beads may'vary widely depending on the permissable degree of perturbal tion. of'.wave propagation. Thuswhile l have described =above the principles of myinvention inconnection with ,specific apparatus, itis/ato be clearlylunderstood that this description is inadeyonly by way of example `andnot as -a limitation to the scope of my invention .as set forth in theobjects thereof and the accompanying claims.

What we claim is: lf. In:` a microwave transmission sys-tem, means forcoupling energy from a coaxial line,.to a line conductor capable of`microwave surface propagation by means of through a turnbuckle1=7=to-asupport (not shown). rI'he an electromagnetic fieldv formed thereabout,said means comprising a hollow conductor extendingfrom the outerconductor of the coaxial line, said lline conductor being extended intosaid hollow conductor, said hollow conductor. being decreased graduallyin thickness toward the end remote from the coaxial line, whereby theconductance thereof is gradually' decreased and insulating material.disposedy about said line` conductor withiny said hollow conductor toconstrict. substantially the radial extent of. the electromagnetic el'das it is propagated from the 'coaxial' line tothe line conductor.

2. I'n` ai microwave transmission system according to claim l, whereinsaid quantity of insulation is decreased gradually in insulatingcharacteristic for a given distance outwardly along said line, after theterminationof said hollow conductor. I

3". The microwave' transmission system according to claim 1, and'further comprising insulatingV material, in-

References Cited in the file of this patent UNITED STATES PATENTS2,207,845 Wolff July 16, 1940 2,269,991 Scheldorf Jan. 13, 19422,438,795 Wheeler Mar. 30, 1948 2,453,759 Robinson Nov. 16, 19482,471,732 Feenburg May 31, 1949 2,491,601 Bernstein et al Dec. 20, 19492,492,404 Streib et al Dec. 27, 1949 2,588,610 B'oothroyd Mar. l1, 19522,685,068 Goubau July 27, 1954 OTHER REFERENCES Principles .and Practiceof Wave Guides, L. G. H. Huxley 1947, MacMillan Co., N. Y., pp. 198-203.(Copy in Scientic Library.)

